Materials whose chemical structures are comprised of molecules linked by covalent bonds into extended structures may be placed into two classes: (1) polymers and cross-linked polymers, and (2) covalent organic frameworks (also known as covalently linked organic networks).
The first class, polymers and cross-linked polymers, is typically embodied by polymerization of molecular monomers to form long linear chains of covalently-bonded molecules. Polymer chemistry processes can allow for polymerized chains to, in turn, or concomitantly, become ‘cross-linked.’ The nature of polymer chemistry offers poor control over the molecular-level structure of the formed material, i.e. the organization of polymer chains and the patterning of molecular monomers between chains is mostly random. Nearly all polymers are amorphous, save for some linear polymers that efficiently pack as ordered rods. Some polymer materials, notably block co-polymers, can possess regions of order within their bulk. In the two preceding cases the patterning of polymer chains is not by design, any ordering at the molecular-level is a consequence of the natural intermolecular packing tendencies.
The second class, covalent organic frameworks (COFs), differ from the first class (polymers/cross-linked polymers) in that COFs are intended to be highly patterned. In COF chemistry molecular components are called molecular building blocks rather than monomers. During COF synthesis molecular building blocks react to form two- or three-dimensional networks. Consequently, molecular building blocks are patterned throughout COF materials and molecular building blocks are linked to each other through strong covalent bonds.
COFs developed thus far are typically powders with high porosity and are materials with exceptionally low density. COFs can store near-record amounts of argon and nitrogen. While these conventional COFs are useful, there is a need, addressed by embodiments of the present invention, for new materials that offer advantages over conventional COFs in terms of enhanced characteristics.
The properties and characteristics of conventional COFs are described in the following documents:
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